1. Field of the Invention
The present invention relates generally to instruments for rotating tools and, more particularly, to apparatus for transmitting rotational motion and torque to a tool.
2. Description of the Prior Art
Several types of powered surgical instruments are commonly used during the performance of orthopedic surgical procedures. The instruments rotate tools which are adapted to engage and shape human bone. Three common types of powered instruments used during performance of orthopedic surgery are drills, reamers and screwdrivers.
As in nonmedical applications, drills are used to form bores in bone. The drilling operation requires a powered instrument that is capable of rotating a drill bit at a relatively high rate of speed.
Powered reamers are used generally to shape certain areas of bone. The bit of a reamer usually defines a relatively large cutting surface and, accordingly, contacts and cuts a relatively large area of the bone. Reaming, therefore, requires a greater amount of torque than drilling. The speed with which the reaming bit is rotated must be less than that at which a drill bit is rotated.
A powered screwdriver instrument is used to insert fasteners into bone. The screwdriver bit of a powered screwdriver must be rotated at a speed that is lower than that at which a drill bit is rotated and, generally, can be rotated at about the same speed as that at which reaming bits are rotated. Unlike the reaming bit, the torque exerted on the screwdriver bit as it is driving a fastener into bone must be limited. Due to this requirement, a powered screwdriver should include a torque limiter to ensure that the fastener is not overdriven into the bone.
In addition to drills, reamers, and driving fasteners the power instrument can be used with other types of tools which require the power instrument to receive through the rear of the power instrument articles for insertion into the surgical site. Therefore, the power instrument must be cannulated.
The varying characteristics of the rotational motion which must be transmitted to drilling, reaming and screwdriving bits have prompted workers in the art to provide a different surgical instrument for performing each type of surgical procedure described above. Because more than one type of procedure must be employed commonly during the course of an operation, the orthopedic surgeon must substitute one instrument for another continually, at great inconvenience to the surgeon.
Accordingly, there is a need for a surgical instrument that can deliver rotational motion at varying speeds and varying torque. Further, there is a need for such an instrument that includes a torque limiter.